Since the magnetic permeability of high manganese content deformed reinforcing bars that have an austenite microstructure is low, such deformed reinforcing bars are used in locations where the magnetic field due to current cannot be disturbed, such as in reinforced structural members in a magnetic resonance imaging (MRI) room of a hospital. Deformed reinforcing bars are used after being bent into a predetermined shape, such as a hoop, during work at a construction site. FIGS. 1A and 1B illustrate examples of the shape, as seen from the side, of a deformed reinforcing bar bent into an approximately square hoop shape. No problem is posed if the reinforcing bar fits within substantially the same plane, as in FIG. 1B, but if out-of-plane deformation occurs, as in FIG. 1A, the reinforcing bar cannot be disposed on a plane surface. Therefore, deformed reinforcing bars are required not to exhibit out-of-plane deformation.
Considering adhesion to concrete, a deformed reinforcing bar is formed as a round bar material having ribs extending in the longitudinal direction around the bar and having predetermined joints. FIG. 2 illustrates an example shape. The diameter of the portion excluding the joints and the ribs, the height of the joints, the distance between joints, the total width of the ribs, and the angle between the joints and axis are determined by JIS standards.
To improve the bending workability of a deformed reinforcing bar, JP H06-288038 A (PTL 1), for example, proposes a reinforcing bar that has joints skewed relative to the axis of the reinforcing bar, with the amount of uplift during bending being improved by controlling the shape and placement of the joints.
JP 2011-208257 A (PTL 2) discloses a high-strength reinforcing bar that has four ribs continuous in the longitudinal direction, arranged at 90° intervals in the circumferential direction of the reinforcing bar, and that has joints connecting ribs adjacent in the circumferential direction. In this reinforcing bar, the bending workability and concrete adhesion are improved by controlling the shape of the ribs and the joints.